The present invention relates to a light scanning device utilizing at least one lens for scanning a plane by irradiating the plane with laser light.
An optical scanning system utilizing a rotating polygonal mirror as shown in FIG. 1 is known for use in light scanning devices such as a laser printer, laser reader and the like. A rotating polygonal mirror 1 rotates in the direction indicated by an arrow A and effects scanning of a laser light 4 on a screen 3. A lens 2 is arranged in the optical path for focusing the laser light into a minute light spot. The rotating polygonal mirror 1 consists of a plurality of highly polished mirror facets or sections 1--1. However, the polishing precision and the directional precision of each mirror facet with respect to the rotational axis must be kept high, which inevitably results in high cost for the device.
It is also known to dispose a hologram on a rotating disc as described, for example, in "HOLOGRAMPHIC GRATING SCANNERS WITH ABERRATION CORRECTIONS", by W. H. Lee, Applied Optics Vol. 16, No. 5, pg. 1,392 (1977). However, the hologram with a rough or rugged surface which is somewhat problematical generally has a low diffraction efficiency at about 30% or below. Although a volume hologram is high in diffraction efficiency, dichromated gelatine is generally used for its structural material and has a weak or small dampness property which is unacceptable for handling purposes.